As the development of petrochemical industry and fine chemicals, the oxygen-containing organic compound has become a very important intermediate. The epoxidation of olefin using hydrogen peroxide as an oxidizer and using a titanium silicate as the catalyst to prepare an oxygen-containing organic compound satisfies the requirement of green chemistry and the developing idea of atom economy, and thus is a new green technology with great prospect.
Epoxides are generally prepared by the epoxidation of an olefin and hydrogen peroxide in the presence of a catalyst. Currently, the titanium silicate molecular sieves are the most popular catalysts. However, when a fixed bed process is used, the catalyst containing a titanium silicate must be shaped and have sufficient crushing strength; otherwise, the catalyst is ready to crush during use to form fine particles or powder. The crushed catalyst on one hand can result in increased pressure drop of the catalyst bed, so as to increase the production cost and also increase the production danger; on the other hand, if the crushed catalyst is carried over by the reaction product, it will result in the lose of catalyst and complex separation of products.
In order to increase the crushing strength of the catalyst, the conventional shaping of titanium silicate molecular sieves increases the catalyst strength depending mainly on increasing the amount of the binder. However, the increased amount of the binder will necessarily result in decreased content of the titanium silicate in the catalyst, namely decreasing the effective active component per unit weight of catalyst, so as to decrease the activity of the catalyst, which in turn decreases the availability of the reactor and increases the equipment cost and the operation cost.
CN101274922A discloses a process of preparing propylene oxide, which process prepares propylene oxide by the epoxidation of propylene using hydrogen peroxide as the oxidizer in the presence of a solvent; wherein the active component of the catalyst used by the process is a titanium silicate having a MFI structure. The crystal grain of the titanium silicate has a hollow structure, with a radial length of 5-300 nm for the cavity portion of the hollow grain. The adsorption capacity of benzene measured for the molecular sieve sample under the conditions of 25 degrees C., P/P0=0.10 and 1 h of adsorption time is at least 70 mg/g, and there is a hysteresis loop between the adsorption isotherm and the desorption isotherm for nitrogen adsorption by the molecular sieve at a low temperature. However, the mass fraction of the titanium silicate in the catalyst used by the patent is 70%, and the selectivity for propylene oxide is only 72.5%. Therefore, the activity of the catalyst used in the process of preparing propylene oxide disclosed by the patent needs to be further increased.
U.S. Pat. No. 6,740,764B1 discloses a process of epoxidising olefin, comprising catalyzing the epoxidation of propylene and hydrogen peroxide using a catalyst containing a titanium silicate and an amorphous silica bonded to said titanium silicate molecular sieve. The patent discloses that a material containing at least elements Si and Ti and a crystalline silicate phase can be reacted with a silane and/or a silane derivative, so as to join together the amorphous silica and the crystalline silicate phase via a chemical bond; however, by calculation of the ratio between the titanium silicate and tetramethoxyl silane charged in the Examples disclosed by the patent, it can be seen that even if tetramethoxyl silane hydrolyzes completely, the content of amorphous silica in the finally obtained catalyst is about only 20 wt % (namely, with too high content of the binder).
In summary, it is still a problem to be solved about how to increase the content of molecular sieve in the catalyst as highly as possible to increase the catalytic activity of the catalyst, provided that the sufficient crushing strength of the catalyst is ensured.